Oil and gas exploration is a risky, complex task that involves sophisticated equipment and substantial financial resources. Whether on land or at sea, a search for oil and gas commences with the drilling of a well. A well may reach a depth of over a mile, or, in the case of ultraheavy rigs, may reach more than six miles in depth.
Once a well is drilled, a technique known as well logging (or wireline logging) provides valuable information about the well, specifically about the likely presence of hydrocarbons nearby. Traditionally, wireline logging was performed by lowering a measuring device known as a sonde down the well. A sonde is a metal container, usually a cylinder, which contains various instrumentation used to gather data.
The wireline sonde is lowered to the bottom of the well, at the well bore. Measurements are taken by the sonde as it is being lifted back to the surface of the well. The types of measurements taken may vary widely. Examples of measurements that may be performed include natural radiation emission, reaction to gamma ray or neutron bombardment, sonic, electrical, electromagnetic induction, resistivity, and so on.
With multiple instruments contained within, the sonde is typically heavy enough to be dropped down the well on a cable or wire. The sonde may be pulled back to the surface using a wench or a pulley.
Recently, fiber optic cable has been used as an alternative for obtaining valuable well data. Fiber optic cable may be advantageous because data can be transmitted at a high speed over long distances. Fiber optic cable is non-conductive and thus may be preferable to use in the well over electrical or electromechanical instruments because of the presence of explosive hydrocarbons.
Better yet, the measurements obtained using the fiber optic cable may be immediately transmitted up the well to a receiving system, such as a portable computer. Using techniques such as optical time domain reflectometry (OTDR), fiber optic cables have, in many cases, supplanted traditional mechanisms for obtaining data within the well bore. Transmitting fiber optic cable down a well under pressure, however, may be problematic.
Thus, there is a need for a method of delivering fiber optic cable down a well under pressure.